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On 09/12/2024 13:47, Michael Schwingen wrote:
> On 2024-12-09, The Natural Philosopher  wrote:
>>> I was surprised you'd use MTBF for a component which is expected to
>>> steadily deteriorate due to wear and tear.
>>>
>>> I though MTBF was more a random failure thing.
>>>
>> No it isnt that at all.
>
> MTBF is a measure for the rate of failures *during normal lifetime* - ie.
>
> 1 / failure rate
>
> It is *not* the lifetime of a component. MTBF is a measure for failures
> during the flat part of the bathtub curve. Failures due to end of lifetime
> (like normal, not-premature wearout on a fan) are not part of MTBF.
>
Well yes and no. There is no guarantee that the failures will be
(economically) repairable.
MTBF is a stochastic emergent property of a bunch of items all of which
have a lifetime.

A fan has items inside it, like its bearings.


> https://www.vitecpower.com/technische-daten/the-difference-bet
een-mtbf-and-lifetime/

"According to the information provided earlier, the primary distinction
lies in one encompassing the failure rate of all components, while the
other exclusively focuses on the lifespan of electrolytic capacitors."


> https://www.rs-online.com/designspark/why-l10-life-expectancy-
s-key-for-fan-durability-over-mtbf-ratings

This is full of bullshit

"MTBF estimates the lifespan of a fan’s electronic components, expressed
in millions of hours. In contrast, L10 Service Life, measured in
thousands of hours, is based on the durability of the bearings and
lubrication grease."

So a fan with no electronic components has no MTBF?



> https://www.digi.com/support/knowledge-base/understanding-mtbf
mean-time-between-failures
>


"Furthermore, MTBF specifically excludes wear-out factors"


  Total crap.

"Mean time between failures (MTBF) describes the expected time between
two failures for a repairable system. For example, three identical
systems starting to function properly at time 0 are working until all of
them fail. The first system fails after 100 hours, the second after 120
hours and the third after 130 hours. The MTBF of the systems is the
average of the three failure times, which is 116.667 hours. If the
systems were non-repairable, then their MTTF would be 116.667 hours."

"In general, MTBF is the "up-time" between two failure states of a
repairable system during operation "

It is an academic nicety to make a distinction between repairable and
irreparable subsystems.

In a Triggers broom sort of way a replacement is simply a repair of all
components

I could for example clean the cruft out of a seized fan  Or oil its
bearings.  Or completely replace it.

What matters is how long the repair or the new fan will last. Not
splitting hairs over MTTF versus MTBF


--
Gun Control: The law that ensures that only criminals have guns.

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